Determination of a discoloration which is proportional to quantities of materials is of utmost importance in practice. Paper and thin-layer chromatography, as well as evaluation of chromatograms and electrophoreograms obtained in course of the electrophoretic processes are based on such determinations.
There are known processes and apparatus for the determination of discoloration [are known], in which the intensity of the light passing through plates illuminated by visible or ultraviolet light or the intensity of the light reflected from such plates have been measured. In both cases, i.e. the translumination of the plates or measurement of the light reflected, illumination with a punctiform (narrow-beam) light source (pencil of light) is possible.
The apparatus mostly used for the quantitative evaluation of chromatograms has been the densitometer. The drawback of densitometers is that the determination can only be performed slowly.
In chromatograms, elphograms, autoradiograms and gelectrophoreograms the rate of discoloration of the spot is proportional to the quantity of material precipitated thereon; within the spot the material has a normal distribution (bell curve), i.e. the spot darkens inwardly toward the center.
In investigating the structure of proteins, in the case of a protein of an average molecular weight, the number of amino acid analyses needed for the determination of the complete amino acid sequence can be 3-4 thousand. Similarly, tests must be performed in the course of plant breeding for improvement of a single species to achieve a higher protein or lysine or methionine content. Besides the investigations mentioned earlier, in the course of clinical treatment analysis of amino acid is used for screening tests. When the known apparatus and processes are used evaluation of the results of a considerable number of tests is time consuming and involves high costs.